Study on Mass Spectrometry for Nonmetallic Elements with Reduced-Pressure ICP

为了在减压下产生电感耦合等离子体，制作了顶部加长的静电屏蔽水冷(ESWC)火炬。还改进了TORCH和质谱仪之间的接口。另加一个旋转泵用于火炬的进一步抽真空，在非常宽的操作条件下可以很容易地产生RP-ICP。然而，火炬气压越低，源于Ar气体中的杂质或真空泄漏的本底物种的离子强度就越高。作为取样器材料的铜的离子强度在较低的气压下也观察到了增加。这一事实表明二次放电的增强。通过在ESWC焊枪屏蔽电路中插入电阻，可以抑制来自Ar的分子离子和二次放电。火炬压力比气体流量影响被分析物和多原子离子的强度。在130Torr附近测得的离子强度是常压下的10倍以上，这表明RP-ICP为非金属元素提供了一种灵敏的离子源。用钨丝电热蒸发法将微升水样引入快速等离子体发射光谱仪。在最佳减压下获得的溴和氯的检出限比用AP-ICP获得的低一个数量级。尽管以Na为基质元素进行了基质效应的研究，但分析物离子强度没有明显的降低。从以上结果可以看出，反相电感耦合等离子体质谱在卤素等非金属元素分析中是非常有用的。

In order to generate an inductively coupled plasma (ICP) at reduced pressure (RP), an electrostatically shielded water-cooled (ESWC) torch with a lengthened top was fabricated. A modified interface between the torch and mass spectrometer was also made. An additional rotary pump was used for the further evacuation of the torch.The RP-ICP could be generated easily under very wide operating conditions. The lower the torch pressure was, however, the higher the ion intensity of background species that originated from the impurities in Ar gas or vacuum leakage became. An increase in the ion intensity of Cu that is the material of a sampler was also observed at lower pressure. This fact indicates an enhancement of the secondary discharge. Molecular ions originated from Ar and the secondary discharge could be suppressed by inserting a resistor into the shielding circuit of ESWC torch. The torch pressure rat her than gas flow rate affected the intensities of analyte and polyatomic ions. The ion intensity of I measured at about 130 Torr was more than 10 times higher than that at atmospheric pressure (AP), which suggests that RP-ICP provides a sensitive ion source for nonmetallic elements. Microliter aqueous samples were introduced into the RP-ICP with electrothermal vaporization method using a tungsten filament. The detection limits of Br and C1 obtained at optimal reduced pressure were ca. one order of magnitude lower than those obtained with AP-ICP.Although a matrix effect was investigated with Na as a matrix element, the significant decrease in the analyte ion intensity was not observed. It was found from above results that RP-ICP-MS is very useful for analysis of nonmetallic elements such as halogens.